High resolution lithographic resist and method

ABSTRACT

A negative working resist composition and medium for microlithographic recording comprises a vinyl polymer having aromatic quaternized nitrogen-containing pendant groups. The resist undergoes a transformation from high to low solubility in polar solvents such as water or low molecular weight alcohols upon exposure to electron beams, ultraviolet light, or X-rays. A method for patterning substrates by employing the resist composition is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 481,611, filedApr. 4, 1983, now U.S. Pat. No. 4,456,678, issued on June 26, 1984,which is a continuation-in-part of application Ser. No. 255,936, filedApr. 20, 1981, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to resist compositions for high resolutionelectron beam lithography. More particularly, it is concerned withelectron beam resist compositions, media for electron beam lithography,and a method for electron beam lithography, all based upon ionicpolymers.

Photolithography has been employed for some time in the electronicsindustry for the production of circuit patterns. In known processes, alayer of resist material is applied to the substrate and patterned byexposure to light through a mask which defines the desired pattern. Uponexposure to light, the photoresist changes solubility, becoming eithermore soluble (positive working resist) or less soluble (negative workingresist) in the developer solvent.

Most known positive working resists are polymeric materials whichundergo a degradative reaction upon exposure to yield products which aremore soluble in the developer solvent. Because most positive workingresists function by this mechanism, they tend to be less sensitive thannegative working resists. Negative resists generally function by amechanism involving a radiation-induced increase in molecular weight,usually as a result of cross-linking, to produce a change in solubility.Negative working resists are generally preferred because of theirgreater sensitivity, but often exhibit undesirable swelling upondevelopment due to cross-linking and entrapment of solvent in thecross-linked polymer net. Swelling can be a serious problem inapplications which require high resolution.

In the production of integrated electronic circuit devices bymicrolithography, designs trends are toward increasing the scale ofdevice complexity, and hence the density of circuit patterns, to reducefabrication costs and increases performance. This goal imposes a numberof requirements upon lithographic resist materials employed in themanufacture of such devices, notably resolution, sensitivity and etchresistance.

With increasing miniaturization of circuit patterns, the limit ofusefulness of optical means for exposure imposed by unwanted diffractioneffects is rapidly being approached. Electron beam lithography recentlyhas found increased use in the production of microcircuit devices.Electron beams, by virtue of their shorter effective wavelength andincreased depth of focus, can record information at higher densities andresolution than can light beams. The increasing use of electron beamlithography has spurred recent interest in the search for suitableelectron beam resist materials. While some photoresist materials canalso be used for electron beam lithograph, most cannot. Moreover, sincemany known electron beam resists are positive working and do not havethe sensitivity or etch resistance of negative working resists, thelatter are preferred.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method of patterning onsubstrates comprises the steps of applying a thin film of cationicpolymeric resist material to the substrate, where the polymeric resistconsists essentially of a vinyl polymer having aromatic quaternizednitrogen-containing heterocyclic pendant groups, exposing the coatedsubstrate to actinic radiation to produce a pattern of insolubilizedresist, washing the exposed coated substrate with a developer solvent toremove a portion of the unexposed regions of resist coating from thesubstrate, utilizing the resist as a protective mask to pattern thesubstrate, and removing the resist coating remaining on the substrate.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the sensitivity to electron beam exposure ofseveral cationic polymer resist materials in accordance with theinvention.

FIG. 2 is a graph showing the ultraviolet absorption spectra of a resistmaterial in accordance with the present invention before and afterexposure to electron beam irradiation.

For a better understanding of the invention, together with other andfurther objects, advantages, and capabilities thereof, reference is madeto the following disclosure and appended claims in connection with theabove-described drawing.

DETAILED DESCRIPTION

Cationic polymers useful as microlithographic recording resists in thepresent invention are polymers having a polyvinyl chain with cationicpendant groups. Pendant groups having aromatic ring systems have beenfound to be particularly stable to attack by etchants. Preferredcationic polymers of this invention are vinyl polymers havingnitrogen-containing aromatic heterocyclic ring pendant groups. As usedthroughout this specification and appended claims, the term "aromatic"is meant to denote any cyclic system of atoms having a delocalizedpi-electron structure satisfying Huckel's Rule and having exceptionalstability resulting from such electron delocalization (cf. James B.Hendrickson et al., Organic Chemistry, 3rd Edition, McGraw-Hill, NewYork, 1970, pp. 167-170).

Examples of quaternized aromatic nitrogen-containing heterocyclicsystems contemplated as falling within the scope of this invention anduseful as pendant groups include, but are not necessarily limited to,monocyclic systems such as: ##STR1## and condensed polycyclic systemssuch as: ##STR2##

While shown as unsubstituted ring systems above, pendant groups havingsmall alkyl group ring substituents such as methyl, ethyl, propyl,isopropyl and butyl groups or the like attached to carbon atoms of thering systems are also contemplated as falling within the scope of thepresent invention.

Cationic polymer resists in accordance with this invention havingpendant groups of the types mentioned above are soluble in solvents ofhigh dipole moment such as water or low molecular weight alcoholsbecause of the electrical charge associated with the quaternizednitrogen atom. Solvents such as water, methanol, ethanol, propanol,isopropanol and the like thus serve as effective developer solvents.There is, however, a decrease in such solubility as the carbon contentof the pendant group increases from monocyclic to tercyclic systems, orwhen such ring systems are substituted with alkyl side chains. Thus, forbetter solubility of the polymeric resist material in its chargedquaternized form, unsubstituted monocyclic pendant groups such aspyridinium or diazinium are preferred. Because of superior etchresistance and ease of formulation, cationic polymer resist compositionshaving pendant pyridinium groups are most preferred.

In the formulas indicated above, R is hydrogen or an alkyl groupcontaining from 1 to 12 carbon atoms, inclusive. For reasons alreadystated, there is decrease in solubility of the cationic polymer resistmaterials of this invention as the carbon content of the alkyl groupattached to the quaternized nitrogen atom increases. Smaller R groupssuch as hydrogen or alkyl groups containing up to about 5 carbon atomsare thus preferred.

In cationic polymer resists of the present invention, the positivecharge of the quaternized nitrogen atom is balanced by a negativelycharged counter ion, preferably a halide ion or halogen-containing ionsuch as F⁻, Cl⁻, Br⁻, I⁻ or PF₆ ⁻. Cationic polymer resist materials inaccordance with the present invention are conveniently prepared bypolymerization of the appropriate vinyl monomer followed by reaction ofthe resulting molecular polymer with a halogen-containing acid or analkyl halide to produce the quaternized nitrogen cationic polymer.Details of the preparation of several poly(vinyl-N-alkylpyridinium salt)cationic polymers are given as illustrative examples below.

Examples of cationic vinyl polymer resist materials of this inventioninclude polymers having the repeating unit ##STR3## where Ar⁺ isselected from ##STR4## with R₁ being selected from hydrogen and the C₁to C₁₂ branched and unbranched alkyl radicals; R₂ being selected fromhydrogen and the C₁ to C₄ branched and unbranched alkyl radicals; and X⁻being selected from F⁻, Cl⁻, Br⁻, I⁻, and PF₆ ⁻.

Cationic polymer resist materials of this invention undergo asubstantial change in solubility in solvents of high dipole moment, suchas water or low molecular weight alcohols, upon exposure to actinicradiation such as ultraviolet light, X-ray, or electron beam. Althoughthe exact mechanism of the change is not well understood, and no theoryis adhered to at the exclusion of others, it is believed that the changeis attributed to a change in the polar character of the polymer from acharged form to an uncharged or neutral form. As detailed below inExample XIX and shown in FIG. 2, the resist materials undergo a changein their ultraviolet spectrum upon irradiation by electron beams,indicating the formation of a less polar species.

In this manner, the resist compositions of the present invention differfrom prior art negative working resist materials which function by achange in molecular weight, usually due to cross-linking, for a changein solubility. Resist compositions of the present invention thus undergoa transformation in kind, i.e. from ionic to non-ionic, upon exposurerather than a change in degree, i.e. a change in molecular weight, as ischaracteristic of most prior art negative-working resist compositions.As a result, the resist compositions of this invention exhibit goodcontrast and differential solubility upon exposure.

The average molecular weight of cationic polymers useful as resistcompositions herein ranges between about 5000 to about 100,000. Becauseof the charge associated with each monomer unit of the cationicpolymers, there seems to be little effect upon the solubility in polarsolvents as the molecular weight of the polymer varies. For particularapplications, the molecular weight range is tailored to obtain desirablefilm-forming qualities of the polymers.

To prepare microlithographic recording media of the invention, asolution of the polymer in water or a low molecular weight alcohol suchas methanol is cast or spun on a substrate to obtain a thin uniformfilm. After depositing the solution on the substrate, which may be anyconventional lithographic support such as glass, plastic, siliconsubstrates and the like, the solution is dried to yield a thin film ofthe polymer. Film thicknesses are varied to suit the particularapplication, but films of up to about 1 μm in thickness are effective asmicrolithographic recording media. Solutions of about 2 weight percentto about 10 weight percent cationic polymer in water or alcohol areeffective in producing dried films of adequate thickness.

Following the casting and drying of the polymer film on the substrate,the film is exposed to actinic radiation. The method of exposure may beby flooding the cast film with the radiation through a patterned mask toreplicate the pattern in the exposed film, or by tracing out the desiredpattern by exposure to an electron beam controllably deflected toproduce the pattern in the film. Exposure may be by ultraviolet light,X-ray, or electron beam in the cases of flood exposure through a patternmask, or by deflected tight electron beam in the case where the patternis traced. Examples XII-XVII below illustrate the effectiveness ofseveral poly(2-vinyl-N-alkylpyridinium iodide) resists in accordancewith the invention when exposed by ultraviolet light and electron beam.

In a preferred embodiment of the invention, cationic polymer resists areexposed by electron beam in a vector scanning electron microscope. Thismethod yields the requisite resolution and density of pattern to producevery large scale integrated electronic circuit patterns on substrates.

As shown by Examples XIII-XVIII and illustrated in FIG. 2, exposure ofseveral poly(vinyl-N-alkylpyridinium iodide) resist materials of thisinvention to a 20 kV electron beam with current densities ranging up toabout 50μ coulombs/cm² were sufficient to insolubilize better than 70%of the resist film applied initially to the substrate in each case. Inparticular cases, exposures at much lower levels were effective.

Following exposure of the polymer film, the unexposed portion ofcationic polymer film is removed by washing the substrate and film in adeveloper solvent of high dipole moment. Water, methanol, or other lowmolecular weight alcohols or organic solvents having a dipole momentgreater than about 1.5 D are effective in removing the unexposedcationic polymer film while leaving the major amount of exposed film onthe substrate.

Regions of the substrate not covered by the resist film remaining on thesubstrate are next processed to produce a pattern in the substrate. Inthe particular application where etched microelectronic circuit patternsare produced in a metallic substrate, the etching step may be carriedout by plasma etching. The cationic polymer resists of this inventionare particularly stable to attack by plasma arc as illustrated byExample XVIII where the etch resistance ofpoly(2-vinyl-N-methylpyridinium iodide) in accordance with the inventionis compared to that of a prior art electron beam resist material notedfor its etch resistance.

One surprising and beneficial aspect of cationic polymer resistmaterials of this invention is the apparent lack of any need to depositan electrically conductive layer either over or under the polymer filmwhen it is deposited on a substrate and employed as an electron beamresist. It is a common practice in electron beam lithography to deposita thin film of electrically conductive material such as a metal film ora layer of tin oxide or indium oxide either over or under the electronbeam resist to dissipate the charge which otherwise tends to build up inthe resist film during electron beam exposure. If this charge is notremoved, the possibility arises of electrostatic deflection orbroadening of the electron beam at the point of impact on the film andsubstrate resulting in diminished resolution. Cationic polymer resistfilms of the present invention appear to have sufficient inherentelectrical conductivity to carry away such charge during exposure,eliminating the need for the deposition of a metal or metal oxide filmon the substrate. This desirable property of the resists of theinvention simplifies the production of microelectronic circuit devicesby eliminating several steps thereby in the overall process. Employingcationic polymer resist compositions of the present invention andelectron beam lithographic methods, microelectronic circuit patternshave been obtained with sub-micron line widths and resolution.

In order to enable one skilled in the art to better practice the presentinvention, the following Examples are provided. It is to be understood,however, that the Examples are merely illustrative of the invention andare not to be viewed as limiting the scope thereof.

Examples I-XI illustrate methods of preparing cationic polymer resistcompositions of the invention. In general, the methods includepolymerization of the appropriately substituted vinyl monomer to producea molecular polymer product. The molecular polymer is treated with ahalogen-containing acid or an alkyl halide to quaternize the nitrogenatom of the aromatic nitrogen-containing heterocyclic pendant group toobtain the desired cationic polymer resist material.

EXAMPLE I

This Example illustrates the general method employed to producemolecular polymers used as intermediates in the formulation of cationicpolymer resist compositions.

Thirty ml of freshly distilled vinyl pyridine were mixed with 0.2 g ofbenzoyl peroxide. The mixture was out-gassed by repeated freezing andthawing under vacuum in a liquid nitrogen bath. After the mixture hadbeen thoroughly out-gassed, it was allowed to warm to room temperatureand stand for 67 hours at 40° C. to polymerize.

At the end of this time the black residual mass was purified by repeatedwashing with tetrahydrofuran from which the polymer was precipitatedeach time with hexane or heptane. The final product has an off-whitecolor.

EXAMPLE II

Five grams of poly(2-vinylpyridine) were dissolved in 50 ml of methylenechloride. To this mixture were added dropwise with stirring a solutionof 11.39 g (0.08 mole) of methyl iodide dissolved in 10 ml of methylenechloride. The resulting mixture was stirred overnight at ambienttemperature. At the end of this time the supernate was decanted from therubbery mass of poly(2-vinyl-N-methylpyridinium iodide) which hadprecipitated from solution.

The product was dried in vacuum overnight. Differential scanningcalorimetry of the produce indicated an endothermic melting transitionpoint of 205° C. and a decomposition temperature of about 500° C.

EXAMPLE III

Poly(2-vinylpyridinium hydrochloride) was prepared by the general methoddetailed in Example II by reacting 4.8 g of poly(2-vinylpyridine) with3.8 ml of 12 molar HCl.

EXAMPLE IV

Poly(2-vinylpyridinium hydrobromide) was prepared by the general methodof Example II by reacting 5.0 g of poly(2-vinylpyridine) with 7.9 ml of49 weight percent hydrobromic acid.

EXAMPLE V

Poly(2-vinylpyridinium hydrofluoride) was prepared by the general methoddetailed in Example II by reacting 1.1 g of poly(2-vinylpyridine) with 2ml of about 48 weight percent hydrofluoric acid.

EXAMPLE VI

Poly(2-vinylpyridinium hexafluorophosphate) was prepared by the generalmethod of Example II by reacting 1.14 g of poly(2-vinylpyridine) with1.6 g of hexafluorophosphoric acid.

EXAMPLE VII

Poly(2-vinyl-N-ethylpyridinium iodide) was prepared by the generalmethod of Example II by reacting 3.28 g of poly(2-vinylpyridine) with4.88 g of ethyl iodide. It was found necessary to heat the methylenechloride solution under reflux for about 24 hours to insure reactionbetween the reagents.

EXAMPLE VIII

Poly(2-vinyl-N-propylpyridinium iodide) was prepared by reacting 5.2 gof poly(2-vinylpyridine) with 8.34 g of n-propyl iodide in methylenechloride. The cationic polymer product was precipitated from solution byaddition of hexane.

EXAMPLE IX

Poly(2-vinyl-N-butylpyridinium bromide) was prepared by reacting 5.14 gof poly(2-vinylpyridine) with 6.70 g of 1-bromobutane in methylenechloride solution. The yellow cationic polymer product was precipitatedfrom solution by the addition of cyclohexane.

EXAMPLE X

Poly(2-vinyl-N-heptylpyridinium iodide) was prepared by reacting 1.2 gof poly(vinylpyridine) with 2.65 g of 1-iodoheptane in methylenechloride solution. The methylene chloride solution was stirred atambient temperatures overnight after which time it was heated underreflux for 2 hours. The polymer was separated by pouring the mixtureinto hexane. The resulting precipitate was dried under vacuum overnight.

EXAMPLE XI

Poly(2-vinyl-N-dodecylpyridinium iodide) was prepared by reacting 4.9 gof poly(2-vinylpyridine) with 13.8 g of dodecyl iodide in methylenechloride. The mixture was stirred at ambient temperatures for 4 days.After this time, the mixture was poured into hexane and the powderedpolymeric product separated. The precipitated polymer was filtered anddried under vacuum overnight.

EXAMPLE XII

This example illustrates the use of cationic polymer resists of thepresent invention in processes employing ultraviolet light exposure.

A film of poly(2-vinyl-N-methylpyridinium iodide) approximately 8000Ångstrom units in thickness was cast by conventional spinning techniqueson a silicon wafer substrate. The solvent employed for film casting wasdistilled water. The coated wafer was dried and then exposed toultraviolet light of 266 nm wavelength from a Nd:YAG pulsed laser.Following exposure, the coated, exposed silicon wafer was washed indistilled water. Measurement of the remaining film thickness indicatedthat most of the film originally cast on the wafer remained. Areflectance infrared spectrum of the exposed film remaining on thesilicon substrate indicated that absorption bands at 1470 cm⁻¹ and 1435cm⁻¹ were intensified relative to the band at 1512 cm⁻¹ compared withthe pre-exposed film.

In Examples XIII-XVII following, shown in the table, the sensitivitiesto exposure by electron beam of several resist materials of thisinvention were evaluated. In each Example, a thin film of theappropriate resist material was cast on a 2 inch silicon wafer substratewhich previously had been oxidized to produce a thin surface layer ofSiO₂. The films were cast in each Example by applying a few drops of amethanolic solution of the resist and spinning at 2000 rpm to spread thefilm evenly over the substrate. Each cast film was dried by baking at120° C. for about 1/2 hour.

Each coated silicon wafer was exposed to a 20 kV electron beam in avector scan electron beam instrument which was computer controlled.Exposure produced a 9×9 array of rectangles each having a differentexposure by varying the dwell time of the beam on each rectangle. Thebeam current was measured by means of a Faraday cup located in theinstrument and a Keithley electrometer.

The approximate minimum exposure required to fix at least 70% of theresist material to the substrate appears in the Table. As the dataindicate, exposure of the resists of this invention to an electron beamwith current densities of up to about 50μ coulombs/cm² is sufficient tofix at least 70% of the resist.

EXAMPLE XVIII

In this Example, the resistance to plasma etching of a resist materialin accordance with the invention is compared to that of a prior artresist material employed for microelectronic circuit fabrication, knownfor its good etch resistance.

Two 2 inch silicon wafers were coated with electron beam resistmaterials. In one case, the resist was poly(2-vinyl-N-methylpyridiniumiodide), and in the other case a prior art resist formulation. Bothcoated silicon substrates were exposed by methods detailed in ExamplesXIII-XVII above, and then developed to produce a pattern or resistmaterial remaining on the substrate.

The two patterned substrates were then simultaneously etched in a plasmaetcher for five minutes at 200 watts, 6% CCl₄ in He at 430 mTorr; fiveminutes at 150 watts. 4% CCl₄ in He at 420 mTorr; and 7 minutes at 50watts, 10% O₂ in He at 480 mTorr.

                                      TABLE                                       __________________________________________________________________________                                   Exposure for 70%                                                         Casting                                                                            Retention of Resist                            Example                                                                            Resist Material      Solvent                                                                            (μ coulombs/CM.sup.2)                       __________________________________________________________________________    XIII Poly (2-vinyl-N--methylpyridinium iodide)                                                          Water                                                                              ˜100                                     XIV  Poly (2-vinyl-N--isopropylpyridinium iodide)                                                       Methanol                                                                           ˜15                                      XV   Poly (2-vinyl-N--butylpyridinium iodide)                                                           Methanol                                                                           ˜10                                      XVI  Poly (2-vinyl-N--heptylpyridinium iodide)                                                          Methanol                                                                           ˜10                                      XVII Poly (2-vinyl-N--dodecylpyridinium iodide)                                                         Methanol                                                                           ˜40                                      __________________________________________________________________________

Under these conditions, the prior art resist material was eroded at anaverage rate of about 120 Å/min and the resist of this invention at anaverage rate of about 60 Å/min.

EXAMPLE XIX

Two-tenths (0.2) gram of poly(2-vinyl-N-methylpyridinium) iodide weredissolved in 20 ml of distilled water and the solution was used to casta thin film of the polymer on a quartz substrate by slowly evaporatingthe solution. The thickness of the polymer film on the quartz substratewas found to be 6200 Angstrom units (measured by a Nanospec filmthickness monitor.)

The ultraviolet absorption spectrum of the film was measured and appearsas Curve 1 in FIG. 2. The polymer film exhibited a strong absorptionband around 275 nanometers due to pi-pi* electronic transitions. Thecase polymer film was next exposed to electron beam irradiation.Following exposure, the film was found to be quite insoluble in water.The measured ultraviolet absorption spectrum of the irradiated film,appearing in FIG. 2 as Curve 2, exhibits an absorption band around 370nanometers not present in the ultraviolet absorption spectrum of theunirradiated film.

The absorption peak appearing at around 370 nanometers followingirradiation by electron beam is attributed to a charge transfer reactionin the material resulting from the electron beam irradiation. Thematerial was found to be quite insoluble in water following theirradiation, the insolubilization also being attributed to the chargetransfer reaction taking place as a result of electron beam irradiation.

The polymeric materials of the present invention thus represent anadvance in the state of the art of electron beam lithographic resistmaterials. Whereas prior art materials depend upon cross-linking ordegradation of the material upon irradiation for a change in solubility,the materials of our invention undergo insolubilization upon irradiationby electron beams due to a charge transfer reaction. The distinctadvantage that flows from this fact is the greatly increased resolutionwhich is achievable through the use of the resist materials of ourinvention. When a lithographic resist material depends uponcross-linking or further polymerization to produce insolubilization, acertain amount of swelling of the resist material results. Thisswelling, in turn reduces the degree of resolution which can beachieved. In the current development of very large scale integratedcircuit patterns on integrated circuit "chips", high resolution is notonly desirable but necessary. The materials of our invention undergoinsolubilization without detectable attendant swelling and are thuscapable of high resolution.

Prior art resist materials which depend upon cross-linking or chemicaldegradation for a change in solubility generally require an unsaturatedcarbon-carbon linkage or similar reactive group sensitive to actinicradiation. On the contrary, the materials of our invention are capableof undergoing a charge transfer reaction, but are unreactive towardcross linking or further polymerization upon irradiation by electronbeams because the chemical structures of the polymer resists of ourinvention are organic structures which are saturated (i.e. containsingle bond carbon-carbon linkages, with the exception of the chemicallystable aromatic nitrogen-containing heterocyclic rings.) The absence ofunsaturation in the polymer resist materials of our invention istherefore believed to confer upon these materials stability towardelectron beam induced cross-linking. These materials thus undergo acharge transfer reaction upon irradiation by electron beams rather thana classical cross-linking reaction.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed is:
 1. A method of microlithographic recordingcomprising the steps of(a) applying a thin film of cationic vinylpolymer resist material to a substrate to form a coated substrate, saidcationic vinyl polymer consisting of a repeating unit ##STR5## whereinAr⁺ is selected from the group consisting of: ##STR6## wherein R₁ isselected from the group consisting of hydrogen, and C₁ to C₁₂ branchedand unbranched alkyl radicals, R₂ is selected from the group consistingof hydrogen and C₁ to C₄ branched and unbranched alkyl radicals, and X⁻is selected from the group consisting of F⁻, Cl⁻, Br⁻, I⁻, and PF₆ ⁻,said polymer having an average molecular weight from about 5,000 toabout 100,000, and said polymer being converted by actinic radiationfrom a charged form soluble in solvents of high dipole moment to anuncharged form insoluble in solvents of high dipole moment; (b) exposingsaid thin film of cationic polymer resist material of the coatedsubstrate to actinic radiation so as to form a pattern of exposedregions and unexposed regions in said thin film, the cationic polymerresist material of the exposed regions being converted by said actinicradiation from a charged form soluble in solvents of high dipole momentto an uncharged form insoluble in solvents of high dipole moment; (c)washing the coated substrate having said pattern of exposed regions andunexposed regions in said thin film in a solvent of high dipole momentto remove the cationic polymer resist material of the unexposed regionsfrom the coated substrate; (d) patterning the washed substrate byutilizing the cationic polymer resist material of the exposed regions asa protective mask to pattern the substrate; and (e) removing anyremaining cationic polymer film from said substrate.
 2. A method formicrolithographic recording in accordance with claim 1 wherein said stepof exposing comprises exposing said thin film of cationic polymer resistmaterial to a directed electron beam to produce said pattern of exposedregions and unexposed regions in said thin film.
 3. A method ofmicrolithographic recording in accordance with claim 2 wherein said stepof exposing said thin film of cationic polymer resist material comprisesexposing to a beam of electrons at a current density of up to about 50microcoulombs/cm².
 4. A method of microlithographic recording inaccordance with claim 1 wherein said step of exposing comprises exposingsaid thin film of cationic polymer resist material to ultraviolet lightof wavelength less than about 300 nanometers.
 5. A method ofmicrolithographic recording in accordance with claim 1 wherein said stepof exposing comprises exposing said thin film of cationic polymer resistmaterial to X-rays.
 6. A method for microlithographic recording inaccordance with claim 1 wherein said step of patterning comprises plasmaetching.